The present invention relates to the aerodynamic stabilization of an air-dropped article and more particularly to an improved housing for stabilizing the free-fall descent of an ocean-deployed sonobuoy after being launched from an aircraft.
Sonobuoys have long been launched from aircraft and deployed to ocean environments for the purpose of underwater surveillance. In order to assure that the sonobuoys reach the water surface accurately and without damage, it has been common practice to employ parachutes or rotochutes to stabilize and control the air descent of these ocean-deployed sonobuoys.
Parachutes have been used successfully in the deployment of the sonobuoys from fixed-wing surveillance aircraft flying at moderate altitudes in the range of 10,000 feet. For high-altitude launches, however, parachute descent of the sonobuoys has been excessively slow, adversely delaying the initiation of monitoring by the buoys and prolonging their overall time required to detect and transmit signals in the water. These parachute deployments from high altitudes are also prone to wind-drift problems that jeopardize accurate placement of the sonobuoys. Furthermore, in launches at lower altitudes from helicopters, which have become an increasingly popular and effective aircraft for surveillance operations, such parachute-equipped sonobuoys present a serious hazard to flight safety due to the high risk of parachute entanglement with either the tail rotor or engine inlet at launch.
Rotochutes, on the other hand, have been safely used to deploy those sonobuoys launched from helicopters. However, the flight-stabilizing rotochutes, have spring-loaded blades that swing outwardly from the sonobuoy for rotation, have only been effective on light-weight buoys at lower altitudes and airspeeds due to the damaging effects of excessive aerodynamic forces on the blades and rotational bearings. These limitations, as well as a relatively high cost of manufacturing, have generally prohibited continued use of rotochutes in the ocean-deployment of air-dropped sonobuoys.
Recently developed sonobuoys have been designed for rapid deployment without any descent retardation equipment. In these cases, stabilization of a free-falling sonobuoy has been effected by means of aerodynamically-designed housings having external stabilizing appendages, such as tail fins. While such aerodynamic housings have been generally satisfactory in stabilizing the free-fall descent of the air-dropped sonobuoy, they have not been totally successful in maintaining vertical attitude and, as a result, have not eliminated the substantial risk of mechanical damage to the sonobuoy upon water entry.